It is often desirable to locate the position of objects moving beneath the surface of the ocean. Fishermen wish to track the positions of large schools of fish; the military wishes to detect the presence of underwater activity such as submarine and diver movement; oceanographers desire to locate underwater eddies and currents. Unfortunately, such underwater activity typically cannot easily be detected from the surface of the ocean.
A major problem which commercial fishing fleets constantly confront is the inability to locate schools of fish. The location of migratory schools of fish presently involves a great deal of guess-work and intuition. Great efforts have been expended to more determinatively locate the position of highly migratory schools of fish such as tuna. For instance, water temperature and currents may be measured and analyzed in order to provide possible indications of areas of the sea in which a school might be found. Known positions of schools in the past are often, used as indications of the present position of the schools. Data is subjected to computer analysis in order to provide more determinative results. However, since little is known about the migration patterns of schools of fish, a fishing captain's sixth sense is often far more reliable than data produced from the analysis of the above parameters.
An alternate and more reliable way to locate schools of fish is to actually sense their presence. Sonar or radar is often used to detect the presence of a large school of fish. It is typically impractical to deploy large numbers of such detecting devices because of the large expense involved and the short life span of the devices due to the harshness of the sea environment. Sensing systems are sometimes placed aboard helicopters or other aircraft which fly over the surface of the sea in search of schools of fish, but aircraft are usually prohibitively expensive to operate and can only be in one place at a time.
The U.S. Navy has developed extremely sophisticated techniques and systems for detecting the presence of enemy submarines. The oceans of the world are constantly subjected to surveillance in an effort to detect and track submarine movement. However, these systems are extremely expensive and are not totally reliable in detecting submarines traveling many hundreds of feet below the surface.
The prior art discloses buoys or other bodies requiring external connection (using a wire or line, floatation or anchoring gear, etc.). Prior art devices are generally relatively expensive, and could not reasonably be expected to be expendable or disposable after a one-time use. Some prior-issued United States patents related to the present invention include U.S. Pat. No. 3,052,205, U.S. Pat. No. 2,968,053, U.S. Pat. No. 3,093,107 and U.S. Pat. No. 4,307,605.
There therefore exists a need for an expedient way to determine the presence of significant underwater activity using inexpensive, expendable sensing devices. A cost-effective system permitting reconaissance of vast areas of the sea to locate spots of relatively high underwater activity (such as that created by migratory schools of fish or the movement of a submarine) could direct a surface fleet to travel directly to the location of the activity. A low cost means of reporting abnormal under-surface activity on a one shot basis from the sea floor (for example, near fish traps and weirs) would also be very desirable.